Dr. Chowne on the Movement of Atmospheric Air in Tubes. 231 



in that with a long limb of 24 inches, from r5 to 9-0, and in that 

 with the long limb of 48 inches, from 3-75 to 140 per minute. 

 The gross number of revolutions in the three tubes, in the nineteen 

 observations, were respectively 5r25, 111'25, and 199"75; and the 

 mean revolutions per minute, 2-697, 5'855, 10-513, which, allow- 

 ing for errors of observation, yield the ratios 1, 2, 4 nearly; so that 

 it may be said that the velocity of the revolutions is in a direct ratio 

 to the lengths of the vertical tubes. 



The influence of the conoidal form of the tube being suggested 

 by Dr. Roget as worthy of investigation, a tube (fig. 10), 96 inches 

 long by 3 inches diameter below and 6 inches above, was fitted to 

 a rectangular tube containing the rotating disc D. Another tube 

 (fig. 11) of the same length, 3 inches in diameter throughout, was 



Fig. 10. 



Fig. 11. 



Fig. 12. 



placed near the conical tube as a term of comparison. The revolu- 

 tions of the disc in the conical tube were more rapid than in that of 

 uniform diameter, in the proportion of 8*8 to 3'0. When the posi- 

 tion of the cone was reversed (fig. 12), and the entrance and exit 

 orifices were equal, the revolutions still continued more rapid than 

 in the tube of uniform diameter. 



To determine the influence of the area of the tube on the velocity 

 of the current, four tubes (figs. 13, 14, 15, 16), 96 inches in length 

 in the long, and 4 inches in the short branch, but varying in dia- 

 meter, were placed in the room near each other and simultaneously 

 observed. 



In a tube of 3 inches uniform diameter (fig. 13), the revolutions 

 were 30 per minute; in one of 5 inches (fig. 15) 9" 15, and in one 

 of 6'75 inches (fig. 16) 13-15; their respective areas being 7065, 

 15-708, and 21-205. In the conical tube (fig. 14) on its base, 

 whose area was 14-529, the revolutions were 8-8 per minute. It 



